got a question...
my sidepanel fan does the same, sometimes its quiet, but then all of a sudden it goes bezerk, louder and softer, like it has a mind of its own. I caught it the other day running at an unusually slow speed, and i checked my monitor on frontpanel to see if anyone changed the fanspeeds, but it was all set to max... when i give the sidepanel fan a slight tap it goes quiet, but not for long... so i have tapped it quite a few times, after a long time of fustration and irritations, i decided to plug that fan out...
all was good for a while (actually quite a long time) and now recently my other sidepanel fan, (next to the motherboard are starting to make those noises, not as loud as the other sidepanel-fan...
oh and before i forget, dust and other kind of stuff that accumalates on the fan bracket or what ever could be causing the fan to carry extra weight and that can also cause this noise....
i clean my fans with a brush very often...